Log why theme submissions are blocked

[poena]

It would be good to know the reason why a theme upload is blocked.

Having this statistic data would help find where information to theme authors need to be improved, if a requirement perhaps is too strict, or if the tools need to be updated.

​https://make.wordpress.org/updates/2021/02/26/would-stats-dashboards-help-your-team/#comment-5177

[dd32]

In 11033:

Theme Directory: Log theme uploads (Successful new themes, Failures, and Updates) to slack #themereview-firehose channel.

See #5702.

[dd32]

In 11037:

Theme Directory: When logging to Slack, include the Trac changeset for quick reviews.

See #5702.

[dd32]

I think we can call this fixed for now?

While these logs aren't as structured as what we'd need to get proper statistics of which checks are failing, I think they probably suffice for now.

We can always add a dashboard view of the errors over time later on if needed.

[dd32]

In 11038:

Theme Directory: When logging theme upload failures to slack, use a more visible :x: icon for the message.

Also uses a nicer class name for when a check class is namespaced.

See #5702.

[poena]

Yes in my opinion this can be closed as fixed.